Apoptosis occurs during normal cellular development and involves dramatic changes in cellular structure. Disruption of apoptosis may contribute to cancer as well as many other types of diseases. Recently, a human DNA fragmentation factor (DFF45) was identified. DFF is composed of two subunts: DFF40 and DFF45. Cleavage of DFF45, which is mediated by caspase-3, leads to DFF40’s activation as a nuclease. Activation of DFF40 can lead to DNA fragmentation, a hallmark of apoptosis.